The present invention relates to sheet-feeding cassettes and sheet-feeding rollers, and more particularly, to a sheet-feeding cassette apparatus and an associated feed roller apparatus which are removably housed in an image forming apparatus.
Japanese Utility Model Laying-Open No. 23130/1991 discloses a copying machine in which paper-feed cassettes are front-loaded into the apparatus body. The copying machine body incorporates a plurality of cassette housing spaces which open onto the front of the machine. A paper feed cassette is installed into a cassette case (outer case), which then is detachably loaded into one of the cassette housing spaces.
Since each cassette case can house only a given-size feed cassette, cases corresponding to each desired feed cassette size must be provided. However, the number of cases the copying machine can contain at one time is necessarily limited, which becomes inconvenient wherein several sheet sizes are employed. Moreover, a feed cassette when loaded is moved in the horizontal direction, and a feed roller in the machine tends to catch on the uppermost sheet in the feed cassette, causing the sheet to shift horizontally.
Japanese Utility Model Laying-Open No. 21630/1988 discloses an apparatus to prevent horizontal shifting of sheets when a feed cassette is loaded into a copying machine. A feed cassette of the apparatus is slid into the machine body horizontally beneath a feed roller, during which movement the cassette does not contact the roller. Then, after the horizontal loading is completed, the stack of sheets in the feed cassette is raised by a spring member so as to come into contact with the feed roller.
However, the spring members together being of uniform spring constant cannot as such compensate the variety of sheet stack weights which arise according to the size of sheet used. Consequently, the force elevating the sheet stack toward the feed roller may be inappropriate for the stack weight and may degrade the sheet-feeding performance.
Japanese Utility Model Laying-Open No. 23130/1991 discloses a copying machine which comprises a feed roller apparatus for feeding sheets loaded in a feed cassette to a sheet transport path. The feed roller apparatus comprises an axle, and a feed roller, mounted along the middle of the axle, which rides on the uppermost sheet in the feed cassette. When the feed roller is rotated by the axle, the uppermost sheet is supplied to the transport path. The surface layer of the feed roller is formed of a high-friction material such as synthetic rubber. However, after repeated use, the feed roller is subject to wear and must be replaced.
However, the various associated elements disposed in the proximity of the feed roller as mounted mid-axle interfere with the roller, encumbering the replacement operation.